1. Field of the Invention
The present invention relates in general to a rotary-shaft support device constructed to rotatably support a rotary shaft, such as a differential device having a differential casing which rotatably supports right and left output shafts and which is arranged to transmit an input torque to the right and left output shafts. More particularly, the present invention is concerned with lubrication grooves formed to feed a lubricant to mating surfaces of the rotary shaft and a shaft hole in which the rotary shaft is rotatably supported.
2. Discussion of the Related Art
An example of a known rotary-shaft support device constructed to rotatably support a rotary shaft is a differential device including a differential casing which rotatably supports right and left output shafts, right and left side gears coaxial with the output shafts, and a pair of pinion gears meshing with the side gears. The differential device is arranged to distribute an input torque to the right and left side gears. The differential casing has shaft holes in which the output shafts are rotatably fitted. Usually, lubrication grooves to be supplied with a lubricant are formed in the inner circumferential surfaces of the shaft holes.
JP-8-170718A discloses in FIG. 1 an example of helical lubrication grooves. The helical configuration of the lubrication holes is advantageous in that the helical configuration permits flows of the lubricant in the axial direction of the differential casing. For this advantage, the lubrication grooves of helical configuration are widely used.
A recent tendency of use of a lubricant having a high degree of viscosity requires an improvement in the lubricating efficiency of a rotary-shaft support device using such a highly viscous lubricant.